This invention relates generally to the field of disc drive storage devices, and more particularly, but not by way of limitation, to improvements in the detection of head flight characteristics in a disc drive.
Disc drives are commonly used as the primary data storage and retrieval devices in modern computer systems. In a typical disc drive, user data are magnetically stored on one or more discs that are rotated at a constant high speed and accessed by a rotary actuator assembly having a plurality of read/write heads that fly adjacent the surfaces of the discs.
When the disc drive is deactivated, the heads are typically moved from an aerodynamically supported position over data recording portions of the discs and brought to rest onto texturized landing zone portions of the discs. More particularly, the heads are said to xe2x80x9ctouchdownxe2x80x9d onto the landing zones as the disc rotational velocity decreases to a level just insufficient to continue to aerodynamically support the heads. Once the heads are located over the landing zones, a latch secures the actuator assembly to prevent inadvertent movement of the heads out onto the data recording portions of the disc as a result of a mechanical shock to the deactivated disc drive.
Upon subsequent reinitialization of the drive, current is applied to a spindle motor to accelerate the discs to operational velocity and the heads xe2x80x9ctake offxe2x80x9d from the landing zones when the discs reach a take off velocity just sufficient to aerodynamically support the heads. The actuator assembly is thereafter unlatched and the heads are moved out over the data recording portions for normal disc drive operation.
It is desirable for a variety of reasons to determine with some precision the respective disc velocities at which the heads take off and touchdown. Heads are typically mounted on xe2x80x9csliderxe2x80x9d assemblies which provide the requisite aerodynamic features that enable the heads to fly above the disc surfaces; hence, head take off and touchdown information is useful in evaluating the performance of various alternative slider designs. Moreover, since disc drives typically use the spindle motors as generators when power is removed from the drives and use this derived power to quickly move the heads to a latched position over the landing zones before the discs come to rest, information regarding head take off and touchdown characteristics is invaluable in configuring the deinitialization operation of new drive designs. Another area where head flight characteristic information is useful is during extended reliability testing where a population of drives is operated over a long period of time to observe changes in operational performance, as disc wear and subsequent disc drive life are typically strongly correlated to the amount of time that the heads spend in contact with the rotating discs before take off and after touchdown.
One prior art approach to determining head take off and touchdown information involves the use of an acoustic emissions (AE) sensor which basically comprises a tiny microphone (transducer) that is bonded to the actuator assembly near the heads. Since a great deal of audible noise is generated as the heads drag along the discs (before take off and after touchdown), and this noise is removed when the heads subsequently separate from the discs, the AE sensor has been used to detect this change in acoustic output and correlate this change to the rotational velocity of the discs.
While operable, this and other similar prior art approaches have suffered from various drawbacks. Insertion of an AE sensor requires that the protective housing surrounding the discs and heads be opened, both allowing for the introduction of contaminants into the housing as well as altering the mechanical configuration of the disc drive. Moreover, using an adhesive to bond the extraneous sensor to the actuator assembly contaminates the drive, making this a destructive test unsuitable for normal manufacturing processes.
Accordingly, there is a need for improvements in the art to enable disc drive manufacturers to evaluate head flight characteristics in a substantially noninvasive and easily implementable manner. It is to such improvements that the present invention is directed.
The present invention is directed to a method for evaluating head flight characteristics in a disc drive.
In accordance with preferred embodiments, a methodology is presented to identify a head take off velocity, which is a velocity just sufficient to aerodynamically support a head above a rotatable disc.
A non-contact voltmeter (NCV) probe is initially brought into close proximity to the disc to form an air gap therebetween, the probe sensing disc potential in relation to a quantity of electrical charge present on the disc. The disc is accelerated with the head initially remaining in contact with the disc, and the disc potential is monitored until a rotational velocity is achieved sufficient to cause the head to separate from the disc and remain aerodynamically supported over the disc. The head take off velocity is thereafter determined in relation to a detected change in the measured disc potential.
A methodology is further provided to determine a head touchdown velocity, which is a velocity at which the head is no longer aerodynamically supportable and comes into contact with the disc. As before, a NCV probe is brought into close proximity to the disc to sense disc potential in relation to a quantity of electrical charge present on the disc.
The disc is accelerated to an initial rotational velocity sufficient to aerodynamically support the head over the disc at a nominal flying height, after which the disc is decelerated to cause the head to come into contact with the disc. The head touchdown velocity is identified in relation to a detected change in the disc potential.
With knowledge of the head take off and touchdown velocities, the distance (in disc revolutions) that the head remains in contact with the disc before take off and after touchdown can be determined.
These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.